Maintain milk yield for summer-grazed cows

PART-time grazing is a good alternative to full-time silage rations for dairy cows. When planned properly, the milk yields of rotationally grazed dairy cows remain as high at pasture as cows fed indoors, according to research conducted at MTT Agrifood Research Finland.

In his doctoral dissertation study, Auvo Sairanen, a senior researcher at MTT Agrifood Research Finland, noted that the principles of feed planning normally used for silage feeding also apply to grazing.

"No particular factor was found in grazing that would significantly differ from silage feeding, as long as the pasture rotation is in order and the forage value of the pasture is taken into account," he said.

The objective of his doctoral dissertation was to seek dietary factors that limit the milk yield of grazing cows.

The study included nine different dietary experiments, with concentrate supplement varying from zero to 12 kg provided twice a day as the cows were milked. With the exception of two experiments, the concentrate was commercially manufactured. In addition to changing the amount of concentrate supplement, the cows had free access to forage at pasture or a forage allowance of between 19 and 25 kg of dry matter per cow per day.

In milk yield experiments, the yield responses to concentrate supplementation were defined, facilitating an economic comparison between grazing and concentrate feeding.

One of the experiments looked into the physiological factors of a diet of freshly cut grass in tie-stall conditions. The flow of nutrients was defined by taking samples from the cow's rumen and omasum. By means of nutrient flow, it is possible to study the processes inside the cow's rumen when the feed contains digestible forage from pasture and a varying amount of concentrate supplement, Sairanen explained.

In addition to these, the use of part-time grazing was studied as a summer feeding strategy. The control group was fed silage indoors full time.

According to the research, the responses to concentrate at pasture were similar to those reported for indoor concentrate feeding. In numerical terms, the response to silage seems to be somewhat higher at pasture than with exclusive silage feeding, considering the high-forage value of the grass from pasture, Sairanen said.

"This can only be explained by the fact that, for some reason or another, a cow cannot intake unlimited amounts of forage from pasture. The physiology of the rumen did not limit the intake of forage, so the limitation must derive from pasture management factors. One example of such factors is that cows have to collect their forage from a large area, whereas in indoor feeding forage is served in one point," Sairanen explained.

Judging by changes in the milk production and liveweight of cows, 20 kg of dry matter per day per hectare at pasture was not enough per cow if the amount of concentrate supplementation was low, but it did not cause any health problems.

Sairanen said it is, therefore, economically sensible to increase concentrate feeding and ensure availability of a sufficient amount of forage from pasture. On the basis of the study, 25 kg of dry matter is a sufficient amount of pasture, but to avoid any risks, the amount of forage from pasture can be even higher.

The responses to concentrate remained the same throughout the lactation period, with the exception of the very end of the period. This means that the proportion of concentrate in the diet can be the same during most of lactation, Sairanen reported. At the end of the lactation, the percentage of concentrate can be reduced to avoid an unnecessary increase in body condition score.

Haylage history

Haylage can present unique ensiling challenges, and taking a closer look at a dairy operation's haylage history helps determine management improvements and inoculant choices to consider this year.

Keeping a close eye on local conditions and silage-making history can help produce high-quality, stable grass and legume silages, said Dr. Renato Schmidt with Lallemand Animal Nutrition.

"Legumes and grasses present different challenges from corn, especially as they are forage crops that might have limitations on soluble sugar content, which is the key to starting fermentation," Schmidt noted. "Plus, you need efficient, specific armies of microbes to produce lactic acid during fermentation to help drop the pH and stabilize the haylage."

Ensiling haylage successfully takes good management, including the right inoculant choices. The use of an inoculant is not a magic bullet to success, he said. If there are no historical problems with feed stability and bunk life, using an independently proven, enzyme-driven homolactic inoculant to control the fermentation and achieve a rapid drop in pH should be sufficient.

"Traditional inoculants that contain strains of homolactic bacteria produce only lactic acid and work in the beginning of the fermentation process," Schmidt said.

On the other hand, a history of challenges with aerobic stability can indicate that an inoculant containing a combination of unique bacteria should be considered. Typical indicators of likely aerobic stability challenges include:

* Silage or total mixed ration heating;

* Aerobic spoilage (e.g., moldy silage patches);

* High dry matter content (35% or more);

* Field damage due to insects;

* Hail or frost damage;

* Fungal disease in the field;

* Drought stress;

* Flood exposure;

* Slow feedout rates, or

* Silage relocation.

Challenges like these can point to the need for greater stability, and combination inoculants can help address those challenges, Schmidt said.

Whether choosing a homolactic or combination inoculant, he recommended that producers look at independent research to support the investment.

"It comes down to the management practices and inoculant choice that work for your operation," Schmidt noted. "Take into account the history of the type of silage you're making, the climate and management. Then, you can choose the elite special forces that best support your management and overcome your challenges."

Indoor housing emissions

Research from Scotland's Rural College (SRUC) has found that greenhouse gas emissions from dairy cattle can be significantly reduced through housing dairy cows all year and breeding them for increased productivity.

The seven-year research project found that in systems where the cows were of high genetic merit (bred for high milk yield) and fed a diet low in forages like silage or grass but boosted by concentrates, greenhouse gas emissions were 24% less than in systems using average herds fed on a high-forage diet, according to an announcement from SRUC.

The reductions are in terms of emissions per unit of milk produced.

The experimental herd was representative of the comparatively small number of herds in Britain that are kept indoors all year. The control cows — those that were of average genetic merit and grazed outside on grass for at least part of the year — are typical of most dairy herds in Scotland.

The research suggests that if these producers switched to a high-genetic merit/low-forage system, there could be big gains in terms of reducing the environmental impact of the dairy sector in Great Britain, SRUC said.

These findings present a conundrum for policy-makers. While the high-genetic merit, indoor route is potentially better environmentally, housing cows year-round is unpopular with many consumers. In addition, early breeding programs that concentrated on yield alone attracted criticism because of concerns over health and welfare issues like lameness and mastitis (although modern breeders now address those issues, recognizing that cow longevity is as important as high milk yield).

The research was carried out as part of a doctoral project by Stephen Ross at SRUC's Crichton Royal Farm and published by SRUC's Rural Policy Centre.

"This project suggests that further genetic improvement of the national herd, combined with low forage feeding, could see greenhouse gas emissions of dairy systems fall substantially," Ross said. "Even if farmers can only make a change in one area, either by improving their animals through breeding or switching to indoor systems feeding low (amounts of) forage, they could still see their emissions fall."

Currently, just 8% of dairy units in the U.K. house their cows throughout the year, and it is only in these systems that a low-forage diet is really practical. In this particular project, the low-forage diet of year-round indoor cows consisted of 50% forage and 50% concentrate. In the high-forage system, cows were grazed in summer months and were housed in the winter and fed a ration that was 80% forage.

There are various reasons why the low-forage/high-productivity combination leads to lower emissions, Ross explained. Simply put, high-yielding cows produce more milk without producing extra emissions, he said. Where cows are housed and fed less forage, more food has to be purchased. However, they need less land and use less inorganic fertilizer, so, again, emissions are reduced.

Balancing pH

If dairy producers could see inside their cows' rumen, they'd see that the environment can fluctuate throughout the day. In fact, it fluctuates quite frequently and for long periods of time. The time spent below a pH of 6.0 is known as subacute rumen acidosis (SARA).

While individual cows do not always show immediate or overt signs, SARA is always present. In fact, costs from SARA are estimated at $1.12 per cow per day, making it recognized as the most important nutritional issue of dairy cattle on a herd basis, according to Anthony Hall with Lallemand Animal Nutrition.

"This period of time is important because a pH of less than six has negative effects on ruminal cellulolytic bacterial activity and fiber digestion," Hall said. "In fact, studies have shown that the rumen environment can be exposed to SARA for up to 11.8 hours daily; that's almost a half a day with impaired digestion."

Even cattle fed total mixed rations and in-feed dietary buffers like sodium bicarbonate are at risk, depending on an individual cow's meal pattern, he noted.

"A cow's rumen pH will vary throughout the day, which can lead to changes in the rumen microbiota and damage the rumen wall," Hall said. "This can mean losses in milk production and feed efficiency. Plus, once cows experience SARA, they can become more susceptible to it if challenged again."

SARA is recognized as a herd syndrome, but the risk is not the same for all cows. There are a number of factors that will predispose fresh, early-lactation, high-yielding and mid-lactation cows to SARA in any herd, Hall explained, noting that probiotic feed additives that improve rumen function and increase fiber digestion can help maximize rumen function in all life stages of dairy cattle.

"Optimizing rumen function can help the modern dairy cow stay ahead of SARA," Hall said. "The benefits to producers can add up to more than just peanuts."